Gas capture process

ABSTRACT

A process for the capture of CO 2  from gas streams, the process including contacting a CO 2  containing gas stream with a compound including: a primary or non-sterically hindered secondary amine group and at least one tertiary amine or sterically hindered secondary amine group; wherein the primary or non-sterically hindered secondary amine and the nearest tertiary or sterically hindered secondary amine group are separated by a carbon chain including 3 or 4 carbon atoms and wherein the compound is a compound of Formula (I).

This application is a U.S. National Stage Application under 35 U.S.C. §371 of International Patent Application No. PCT/AU2012/000409 filed 18 Apr. 2012, which claims the benefit of priority to Australian Patent Application No. 2011901448 filed 18 Apr. 2011, the disclosures of all of which are incorporated by reference herein in their entireties. The International Application was published in English on 26 Oct. 2012 as WO 2012/142668. To the extent appropriate, a claim of priority is made to each of the above disclosed applications.

FIELD OF THE INVENTION

This invention relates to amines and their use in capturing carbon dioxide from gas streams.

BACKGROUND OF THE INVENTION

There is growing pressure for stationary producers of greenhouse gases to dramatically reduce their atmospheric emissions. Of particular concern is the emission of carbon dioxide (CO₂) into the atmosphere. One method of reducing atmospheric CO₂ emissions is through its capture at a point source and subsequent storage in geological or other reservoirs.

The process for capturing CO₂ from power station and other combustion device flue gases is termed post combustion capture (PCC). In post combustion capture, the CO₂ in flue gas is first separated from nitrogen and residual oxygen using a suitable solvent in an absorber. The solvent is usually an aqueous basic mixture containing components that undergo a chemical reaction with acid gases such as CO₂. It might contain amines (e.g. alkanolamines, ammonia, alkylamines) and/or inorganic salts (e.g. carbonate or phosphate). The CO₂ is subsequently removed from the solvent in a process called stripping (or regeneration), thus allowing the solvent to be reused. The stripped CO₂ is liquefied by compression and cooling, with appropriate drying steps to prevent hydrate formation. PCC in this form is applicable to a variety of stationary CO₂ sources including power stations, steel plants, cement kilns, calciners and smelters.

Acid gases, such as carbon dioxide, are also present in natural gas and other pressurised gas streams and need to be removed to meet gas quality specifications. Pressurised gas streams containing CO₂ are also produced in fuel conversion processes such as natural gas reforming and coal gasification combined with a water-gas shift conversion to produce mixtures of hydrogen and carbon dioxide. These gas streams are then suitable for pre-combustion capture of CO₂. The conventional approaches for such removal include membrane separation or amine treatment.

When CO₂ is absorbed into an aqueous solution a number of reactions can occur. The reactions are shown by the following equations where (1) is hydration of gaseous CO₂, (2) is the reaction of CO₂ with water to form carbonic acid, (3) is the reaction of CO₂ with hydroxide to form bicarbonate and (4) and (5) are the carbonic acid-bicarbonate-carbonate acid-base equilibria.

If an amine, or multiple amines, are present in solution a number of additional reactions may occur. If the amine is a sterically free primary or secondary amine such as monoethanolamine (MEA) or diethanolamine (DEA) the following reactions can occur between CO₂ and each amine. Equation (6) is the formation of a carbamate species via a nitrogen-carbon bond formation between the amine and CO₂. This is generally the kinetically fastest reaction of those that occur with CO₂. Equation (7) is the amine acid-base equilibrium. For polyamines the reactions of equation (6) and (7) may occur for each nitrogen atom. For sterically hindered primary or secondary amines the carbamate species is less stable than in sterically free amines which leads to enhanced formation of the bicarbonate species. For tertiary amines only the acid-base equilibrium of equation (7) occurs.

Monoethanolamine (MEA) is currently employed in industrial CO₂ capture but has a number of limitations, including solvent degradation due to oxidation and reaction with nitrogen and sulphur oxides, solvent losses due to high volatility and high energy requirements needed to desorb the CO₂ from the CO₂ loaded MEA. Some other amines used for industrial CO₂ capture have a larger CO₂ absorption capacity than MEA, but have poor rates of CO₂ capture. Slow CO₂ absorption rates are undesirable because to achieve the requisite absorption of CO₂, longer contact times between the CO₂ containing gas stream and the amine means that longer absorption columns and larger capital costs are usually required.

The use of amines as sorbents in CO₂ capture may be limited by the thermal degradation and oxidation of the amines. Much of the research on amine solvents for CO₂ capture is based around formulation with commercially available amines. There appears to be little study of novel amines that are designed, via amine structural modification, to match the characteristic requirement of CO₂ capture. 4-Aminopiperidine has been reported to perform well in CO₂ capture (Singh et al., 2008).

In addition, European patent application no 2036602 (Mitsubishi Heavy Industries, Ltd.) relates to an absorbent liquid for removing CO₂ and/or H₂S from gas which includes compounds which are described in very general terms in the application (for example, by way of very broad general formulae). However, the data in the application showing the CO₂ absorption capacity of the compounds is quite limited.

However, there still exists a need for a more efficient CO₂ capture technology or process for post combustion capture.

It is an object of the present invention to overcome or at least alleviate one or more of the problems associated with the prior art.

Reference to any prior art in the specification is not, and should not be taken as, an acknowledgment or any form of suggestion that this prior art forms part of the common general knowledge in Australia or any other jurisdiction or that this prior art could reasonably be expected to be ascertained, understood and regarded as relevant by a person skilled in the art.

SUMMARY OF THE INVENTION

The Applicants have surprisingly discovered that the compounds of the invention (as represented by formula (I) below) exhibit good molar CO₂ cyclic capacities. The compounds of formula (I), which are derivatives of 4-aminopiperidine, show a higher molar CO₂ cyclic capacity that that of 4-aminopiperidine itself.

Accordingly, in one aspect, the present invention provides a process for the capture of CO₂ from gas streams, the process including contacting a CO₂ containing gas stream with a compound including:

-   -   a primary or non-sterically hindered secondary amine group and     -   at least one tertiary amine or sterically hindered secondary         amine group;         wherein the primary or non-sterically hindered secondary amine         and the nearest tertiary or sterically hindered secondary amine         group are separated by a carbon chain including 3 or 4 carbon         atoms and wherein the compound is a compound of Formula (I)

wherein R¹ is represented by hydrogen, C₂ to C₆ alkanol or C₁ to C₆ alkyl; R² is represented by hydrogen, C₁ to C₆ alkyl, C₂ to C₆ alkanol, —(CH₂)_(n)—NR₆R₇, —(CH₂)_(p)—COOH, —(CH₂)_(p)COOQ, —(CH₂)_(p)-heterocyclic ring containing one to four heteroatoms independently selected from nitrogen, oxygen and sulphur; R³ and R⁵ are independently selected from hydrogen, C₁ to C₄ alkyl, C₂ to C₆ alkanol, —(CH₂)_(n)—NR⁸R⁹; R⁴ is represented by hydrogen, C₁ to C₆ alkyl, C₂ to C₆ alkanol, —(CH₂)_(n)—NR₆R₇, —(CH₂)_(p)—COOH, —(CH₂)_(p)COOQ, —(CH₂)_(p)—SO₃H, —(CH₂)_(p)SO₃Q, —(CH₂)_(p)—PO₃H₂, —(CH₂)_(p)PO₃Q_(s), —(CH₂)_(p)-heterocyclic ring containing one to four heteroatoms independently selected from nitrogen, oxygen and sulphur; x is 0 or 1; n is 2 to 6; p is 1 to 6; Q is hydrogen, a metal ion or R¹⁶R¹⁷R¹⁸R¹⁹N⁺; s is 1 or 2 R⁶ and R⁷ are independently selected from hydrogen, alkyl, alkanol, alkylamine or R⁶ and R⁷ together with the nitrogen atom to which they are attached form a ring structure R⁸ and R⁹ are independently selected from C₁ to C₆ alkyl, C₂ to C₆ alkanol, C₂ to C₆ alkylamine, —(CH₂)_(n)—NR₆R₇, —(CH₂)_(p)—COOH, —(CH₂)_(p)COOQ, —(CH₂)_(p)—SO₃H, —(CH₂)_(p)SO₃Q, —(CH₂)_(p)—PO₃H₂, —(CH₂)_(p)PO₃Q_(s), or R⁸ and R⁹ together with the nitrogen atom to which they are attached form a ring structure; and R¹⁶, R¹⁷, R¹⁸ and R¹⁹ are independently selected from hydrogen or alkyl; with the proviso that when R⁴ is hydrogen, R¹ and/or R² is not hydrogen; when R⁴ is not hydrogen, R¹ and/or R² is hydrogen; when R⁴ and R¹ are both hydrogen, R² is not methyl; and when R⁴ and R² are both hydrogen, R¹ is not methyl.

In a further aspect, the present invention provides a compound including:

-   -   a primary or non-sterically hindered secondary amine group and     -   at least one tertiary amine or a sterically hindered secondary         amine group;         wherein the primary or non-sterically hindered secondary amine         group and the nearest tertiary or sterically hindered secondary         amine group are separated by a carbon chain including 3 or 4         carbon atoms; and         wherein the compound is a compound of Formula (I):

wherein R¹ is represented by hydrogen, C₂ to C₆ alkanol or C₁ to C₆ alkyl; R² is represented by hydrogen, C₁ to C₆ alkyl, C₂ to C₆ alkanol, —(CH₂)_(n)—NR₆R₇, —(CH₂)_(p)—COOH, —(CH₂)_(p)COOQ, —(CH₂)_(p)-heterocyclic ring containing one to four heteroatoms independently selected from nitrogen, oxygen and sulphur; R³ and R⁵ are independently selected from hydrogen, C₁ to C₄ alkyl, C₁ to C₄ alkanol, —(CH₂)_(p)—NR⁸R⁹; R⁴ is represented by hydrogen, C₁ to C₆ alkyl, C₂ to C₆ alkanol, —(CH₂)_(n)—NR⁶R⁷, —(CH₂)_(p)—COOH, —(CH₂)_(p)COOQ, —(CH₂)_(p)—SO₃H, —(CH₂)_(p)SO₃Q, —(CH₂)_(p)—PO₃H₂, —(CH₂)_(p)PO₃Q_(s), —(CH₂)_(p)-heterocyclic ring containing one to four heteroatoms independently selected from nitrogen, oxygen and sulphur; x is 0 or 1; n is 2 to 6; p is 1 to 6; Q is hydrogen, a metal ion or R¹⁶R¹⁷R¹⁸R¹⁹N⁺; s is 1 or 2; R⁶ and R⁷ are independently selected from hydrogen, C₁ to C₆ alkyl, C₂ to C₆ alkanol, C₂ to C₆ alkylamine or R⁶ and R⁷ together with the nitrogen atom to which they are attached form a ring structure R⁸ and R⁹ are independently selected from C₁ to C₆ alkyl, C₂ to C₆ alkanol, C₂ to C₆ alkylamine, —(CH₂)_(n)—NR₆R₇, —(CH₂)_(p)—COOH, —(CH₂)_(p)COOQ, —(CH₂)_(p)—SO₃H, —(CH₂)_(p)SO₃Q, —(CH₂)_(p)—PO₃H₂, —(CH₂)_(p)PO₃%, or R⁸ and R⁹ together with the nitrogen atom to which they are attached form a ring structure; R¹⁴ and R¹⁵ are independently selected from C₁ to C₆ alkyl, C₂ to C₆ alkanol, C₂ to C₆ alkylamine or R¹⁴ and R¹⁵ together with the nitrogen atom to which they are attached form a ring structure; and R¹⁶, R¹⁷, R¹⁸ and R¹⁹ are independently selected from hydrogen or alkyl; with the proviso that when R⁴ is hydrogen, R¹ and/or R² is not hydrogen; when R⁴ is not hydrogen, R¹ and/or R² is hydrogen; when R⁴ and R¹ are both hydrogen, R² is not methyl; and when R⁴ and R² are both hydrogen, R¹ is not methyl.

BRIEF DESCRIPTION OF THE DRAWINGS/FIGURES

FIG. 1 shows a flow-diagram example of a CO₂ capture apparatus that may be employed in the process of one embodiment of the present invention.

FIG. 2 shows the CO₂ absorption and desorption of 1-ethanol-4-aminopiperidine, 1-propyl-4-aminopiperidine, 4-ethanolaminopiperidine, 4-propylaminopiperidine compared with 4-aminopiperidine.

FIG. 3 shows the CO₂ absorption and desorption of 1-ethanol-4-aminopiperidine, 1-propyl-4-aminopiperidine, 4-ethanolaminopiperidine, 4-propylaminopiperidine, 4-aminopiperidine compared with monoethanolamine and piperazine.

DETAILED DESCRIPTION OF THE EMBODIMENTS

As used herein, the term “sterically hindered secondary amine” means that the substituent on the secondary amine has sufficient bulk such that a reaction between the secondary amine and CO₂ produces an unstable carbamate species.

As used herein, the term “alkyl” means a straight or branched chain, or cyclic, saturated aliphatic group, or a combination thereof.

As used herein, the term “alkanol” means a group where an alcohol group (—OH) is bound to a carbon atom, ie, —(CH₂)_(n)OH.

As used herein, the term “alkylamine” means a group where an alkyl group is bound to the nitrogen atom of an amine group.

As used herein, except where the context requires otherwise, the term “comprise” and variations of the term, such as “comprising”, “comprises” and “comprised”, are not intended to exclude further additives, components, integers or steps.

It has surprisingly been found that the compounds used in the process of the present invention, described above, have a higher capacity for CO₂ absorption and good reaction rates in CO₂ absorption, and higher efficiency in CO₂ desorption.

In addition, the compounds have relatively high boiling points which may result in reduced amine evaporation during the process. The reduction in evaporation may be beneficial from cost and environmental impact perspectives.

In one embodiment the present invention provides a compound of Formula (I)

wherein R¹ is represented by hydrogen, C₂ to C₆ alkanol or C₁ to C₆ alkyl; R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); R³ and R⁵ are independently selected from hydrogen, C₁ to C₄ alkyl and C₁ to C₄ alkanol; R⁴ is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and x is 0 or 1; with the proviso that when R⁴ is hydrogen, R² is not hydrogen; when R² is hydrogen, R⁴ is not hydrogen; and when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂,

—(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0;

R¹ is represented by hydrogen;

R² is represented by hydrogen;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen;

with the proviso that when x is 0, R¹ is hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0;

R¹ is represented by hydrogen;

R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0;

R¹ is represented by C₁ alkyl;

R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0;

R¹ is represented by hydrogen;

R² is represented by hydrogen;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 1;

R¹ is represented by hydrogen;

R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 1;

R¹ is represented by C₁ alkyl;

R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0;

R¹ is represented by C₁ alkyl;

R² is represented by —CH₂CH₂CH₃, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0;

R¹ is represented by hydrogen;

R² is represented by hydrogen;

R³ is represented by hydrogen;

R⁴ is represented by —CH₂CH₃, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH or —(CH₂)₂N(CH₃)₂;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0;

R¹ is represented by hydrogen;

R² is represented by —CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH or —(CH₂)₂N(CH₃)₂;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0;

R¹ is represented by C₁ alkyl;

R² is represented by —CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH or —(CH₂)₆OH;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 1;

R¹ is represented by hydrogen;

R² is represented by —CH₂CH₃, —(CH₂)₂OH, —(CH₂)₆OH or —CH₂COOH;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 1;

R¹ is represented by C₁ alkyl;

R² is represented by —CH₂CH₃ or —(CH₂)₂OH;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen;

R² is represented by hydrogen;

R³ is represented by hydrogen;

R⁴ is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH or —(CH₂)₆OH; and

R⁵ is represented by hydrogen.

In a further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃ or —(CH₂)₂N(CH₃)₂;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃ or —(CH₂)₂N(CH₃)₂; and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa or —CH₂COOK;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa or —CH₂COOK; and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R′ is hydrogen and x is 0.

In a further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —(CH₂)₂OH, —(CH₂)₃OH or —(CH₂)₆OH;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —(CH₂)₂OH, —(CH₂)₃OH or —(CH₂)₆OH; and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —CH₂COOH, —CH₂COONa or —CH₂COOK;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —CH₂COOH, —CH₂COONa or —CH₂COOK; and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a still further embodiment, the present invention provides a compound of Formula (I) wherein:

x is 0 or 1;

R¹ is represented by hydrogen;

R² is represented by ethyl, propyl or —(CH₂)₂N(CH₃)₂;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a further embodiment, the present invention provides a compound selected from the group consisting of:

In a further embodiment, the present invention provides a compound selected from the group consisting of:

In a further embodiment, the present invention provides a compound selected from the group consisting of:

In a further embodiment, the present invention provides a compound selected from the group consisting of:

In one embodiment the present invention provides a process wherein in the compound of Formula (I):

R¹ is represented by hydrogen, C₂ to C₆ alkanol or C₁ to C₆ alkyl; R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); R³ and R⁵ are independently selected from hydrogen, C₁ to C₄ alkyl and C₁ to C₄ alkanol; R⁴ is represented by hydrogen-CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and x is 0 or 1; with the proviso that when R⁴ is hydrogen, R² is not hydrogen; when R² is hydrogen, R⁴ is not hydrogen; and when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂₁—(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen;

R² is represented by hydrogen;

R³ is represented by hydrogen;

R⁴ is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen;

with the proviso that when x is O, R¹ is hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0;

R¹ is represented by hydrogen;

R² is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0;

R¹ is represented by C₁ alkyl;

R² is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0;

R¹ is represented by hydrogen;

R² is represented by hydrogen;

R³ is represented by hydrogen;

R⁴ is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole) and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 1;

R¹ is represented by hydrogen;

R² is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 1;

R¹ is represented by C₁ alkyl;

R² is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0;

R¹ is represented by C₁ alkyl;

R² is represented by —CH₂CH₂CH₃, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0;

R¹ is represented by hydrogen;

R² is represented by hydrogen;

R³ is represented by hydrogen;

R⁴ is represented by —CH₂CH₃, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH or —(CH₂)₂N(CH₃)₂;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0;

R¹ is represented by hydrogen;

R² is represented by —CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH or —(CH₂)₂N(CH₃)₂;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0;

R¹ is represented by C₁ alkyl;

R² is represented by CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH or —(CH₂)₆OH;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 1;

R¹ is represented by hydrogen;

R² is represented by —CH₂CH₃, —(CH₂)₂OH, —(CH₂)₆OH or —CH₂COOH;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 1;

R¹ is represented by C₁ alkyl;

R² is represented by —CH₂CH₃ or —(CH₂)₂OH;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a still further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0;

R¹ is represented by hydrogen;

R² is represented by hydrogen;

R³ is represented by hydrogen;

R⁴ is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH or —(CH₂)₆OH; and

R⁵ is represented by hydrogen.

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃ or —(CH₂)₂N(CH₃)₂;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃ or —(CH₂)₂N(CH₃)₂; and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa or —CH₂COOK;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa or —CH₂COOK; and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —(CH₂)₂OH, —(CH₂)₃OH or —(CH₂)₆OH;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —(CH₂)₂OH, —(CH₂)₃OH or —(CH₂)₆OH; and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —CH₂COOH, —CH₂COONa or —CH₂COOK;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —CH₂COOH, —CH₂COONa or —CH₂COOK; and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen or C₁ alkyl;

R² is represented by hydrogen, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole);

R³ is represented by hydrogen;

R⁴ is represented by hydrogen, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and

R⁵ is represented by hydrogen;

with the proviso that when R⁴ is hydrogen, R² is not hydrogen;

when R² is hydrogen, R⁴ is not hydrogen; and

when R² is hydrogen, R¹ is hydrogen and x is 0.

In a still further embodiment, the present invention provides a process wherein, in the compound of Formula (I):

x is 0 or 1;

R¹ is represented by hydrogen;

R² is represented by ethyl, propyl or —(CH₂)₂N(CH₃)₂;

R³ is represented by hydrogen;

R⁴ is represented by hydrogen; and

R⁵ is represented by hydrogen.

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I) is selected from a group consisting of:

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I) is selected from a group consisting of:

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I) is selected from a group consisting of:

In a further embodiment, the present invention provides a process wherein in the compound of Formula (I) is selected from a group consisting of:

When a compound as described above is used in a mixture with another amine, (ie, a mixed amine solution), the CO₂ capture efficiency of the mixed amine solution is also better than that of 4-aminopiperidine used in a mixture with another amine. Without wishing to be bound by theory, it is thought that the compounds described above act as promoters in mixed amine solutions. Accordingly, the cost and energy consumption of CO₂ capture may be lowered by the use of a compound as described above, by itself, or in a mixture with another amine in CO₂ capture.

In the process of the present invention, the compound is typically present in the form of an aqueous solution. The compound may be present in the aqueous solution in an amount of from about 5 to 99 percent by weight, preferably from about 10 to 90 percent by weight, most preferably from about 15 to 75 percent by weight, based upon the total weight of the aqueous solution.

When the compound is used in a mixture with another amine, (ie, a mixed amine solution), the compound may be present in the mixed amine solution in an amount of from about 10 to 100 percent by weight, preferably from about 20 to 80 percent by weight, most preferably from about 30 to 70 percent by weight, based upon the total weight of the amine components.

The optimal amount of the compound used in the process of the present invention will depend upon the gas stream composition, outlet fluid requirement and circulation rate. A person skilled in the art would readily be able to determine the appropriate amount of the compound to use in the process of the present invention.

The process of the present invention may be carried out in conventional equipment for the removal of carbon dioxide from gas streams by reactive chemical absorption and detailed procedures are well known to the person skilled in the art. See, for example, the flow diagram of FIG. 1, or Newman, S. A., Acid and Sour Gas Treating Processes, Gulf Publishing Company, Texas, 1995.

In the embodiment described by FIG. 1, the equipment comprises an absorber column 2, a heat exchanger 5, a desorber column 6 and a reboiler 9. Flue gas, which typically comprises 1-15% CO₂, preferably 5-15% CO₂ and more preferably 10-15% CO₂, is optionally passed through a prescrubber and then passes through conduit 1 to the packed absorber column 2, where it is contacted with the compound of formula (I). Pressure and temperature conditions in the absorber column 2 are typically 1 atm and about 40 to 60° C. CO₂-lean flue gas is released from the top of the absorber via conduit 3. The CO₂-rich solution containing the compound of formula (I) is conducted through a pipe 4 to a desorber column 6 via a heat exchanger 5. In the desorber column 6, the CO₂-rich solution containing the compound of formula (I) is heated to reverse the absorption reaction. Typical pressure and temperature conditions in the desorber are 0.4-15 atm and 75 to 200° C. CO₂ and moisture is collected from the top of the desorber column via conduit 7. The desorber column is heated by means of a reboiler 9, connected to the desorber by conduits 8 and 10. The heat source of the reboiler is preferably low pressure steam at a temperature of 105-135° C., but to achieve higher temperature conditions in the stripper a higher quality steam is necessary, ie, preferably steam with a temperature 5 to 15 degrees higher than the stripper temperature. The CO₂-lean solution containing the compound of formula (I) is then conducted through a pipe 11 to the absorber 2 via the heat exchanger 5. In the heat exchanger 5, sensible heat from the CO₂-lean solution containing the compound of formula (I) is used to heat the CO₂-rich solution from the absorber.

The desorption process which regenerates the compounds of formula (I) may be carried out be any other suitable method known to the person skilled in the art, such as pressure relieving or stripping treatment.

The process according to the present invention may be conveniently carried out in any suitable absorber, including packed, plate or spray towers. These absorbers are interchangeable to a considerable extent although certain specific conditions may favour one over the other.

In addition to conventional packed, plate or spray towers, specialised absorber towers have been developed to meet specific process requirements. Examples of these specific towers include impingement-plate scrubbers and turbulent contact scrubbers.

The process of the present invention may be carried out in either packed, plate or spray towers, or specialised towers developed to meet specific process requirements, and may contain other peripheral equipment as necessary for optimal process operation. Such peripheral equipment may include but is not limited to an inlet gas separator, a treated gas coalescer, a solvent flash tank, a particulate filter and a carbon bed purifier. The inlet gas flow rate varies according to the size of the equipment but is typically between 5 000 and 25 00 cubic meters per second. The solvent circulation rate is typically between 10 and 40 cubic meters per tonne of CO₂. The operating pressure of the absorber is typically between 1 and 100 atm with lower operating pressures being typical of post-combustion CO₂ capture and higher operating pressures being typical of natural gas treatment and pre-combustion CO₂ capture.

In the process of the present invention, a gas stream containing CO₂ at or above atmospheric pressure is contacted with a compound of formula (I) at a temperature at or above ambient temperature, preferably between 30° C. to 60° C., and more preferably between 35° C. to 45° C. to effect absorption of CO₂ from the gas stream. Optionally, corrosion inhibitors, scale inhibitors, antifoam agents and/or other additives known to those in the art that may assist in the CO₂ capture process of the present invention may be employed.

The following examples are offered to illustrate but not to limit the present invention.

EXAMPLES Example 1 Reductive Amination

This method may be used for the synthesis of secondary or tertiary amine product from either (1) or (3) below.

Sodium triacetoxyborohydride, Na(OAc)₃BH (60 mmol) was added potionwise to a stirred solution of tert-butyl 4-oxopiperidine-1-carboxylate (1) or 1-Boc-piperidine-4-carboxaldehyde (3) (30 mmol), acetic acid (30 mmole) and corresponding amine, RNH₂ or RNHMe, (30 mmole) in dichloromethane (60 ml). The reaction was stirred under nitrogen at room temperature overnight. The reaction was then quenched by the careful addition of H₂O or 1M NaOH (60 mL). The pH of the mixture was adjusted to basic (˜pH 10) by the careful addition of solid NaOH and the mixture was stirred for 15-30 min. The organic phase was separated and the aqueous phase was extracted with dichloromethane (2×60 mL). The combined organic phase was washed with H₂O (2×60 mL) and dried by K₂CO₃ or filtration through phase separation paper. Removal of the solvent under vacuum gave the product in excellent yield.

NOTE—the amine hydrochloride salt may be used in the reaction. If the amine hydrochloride salt is used, one equivalent of triethylamine (Et₃N) is used instead of acetic acid.

A detailed description of this method is provided in Ahmed F. Abdel-Magid, Kenneth G. Carson, Bruce D. Harris, Cynthia A. Maryanoff, and Rekha D. Shah; Journal of Organic Chemistry, 1996, 61(11) 3849-3862.

Example 2 Hydrogenation

The corresponding amine (30 mmol) was added to a solution of 1-Boc-piperidine-4-carboxaldehyde (3) (30 mmol) in EtOH (40 ml) followed by 10% Pd/C (50% in H₂O, 0.3 g). The reaction was processed under a hydrogen atmosphere (40 psi) at room temperature until gas uptake finished and reaction completed (˜2-3 hours). The reaction mixture was filtered through celite and the filtrate was evaporated to dryness to give product (6) in excellent yield.

Note: The amine.HCl salt may be used in the reaction. When the amine HCl salt was used an equivalent amount of triethylamine was added. After the above work-up of the reaction, TEA.HCl salt was removed via a partition of dichloromethane-H₂O followed by washing with 5% Na₂CO₃. The organic phase was dried (phase separation paper filtration of K₂CO₃) and concentrated under vacuum to give the product.

A detailed description of this method is provided in WO 2007/018461.

Example 3 Reductive Amination

The following synthesis of amines (5) and (4) start with amines (2) and (6). The synthesis of amine (2) is provided in Example 1 and the synthesis of amine (6) in Example 2.

To a solution of amine (2 or 6) (30 mmole) in dichloromethane (200 mL) was added aqueous formaldehyde (37% in H₂O, 12.2 mL) followed by sodium triacetoxyborohydride (90 mmol) and AcOH (40 ml). The reaction mixture was stirred under N₂ overnight at room temperature. The reaction was quenched by the addition of H₂O or 1M NaOH (100 mL). The pH of the mixture was adjusted to basic (˜pH 10) by the careful addition of solid NaOH. The organic phase was separated and the aqueous phase was extracted with dichloromethane (2×60 mL). The combined organic phase was washed with H₂O (2×60 mL) and dried by K₂CO₃ or a filtration through phase separation paper. Removal of the solvent under vacuum gave the product (5 or 4) in excellent yield.

A detailed description of this method is provided in Kazuhiro Yokoyama, Noriko Ishikawa, Susumu Igarashi, et al; Bioorganic & Medicinal Chemistry, 16 2008, 7968-7974.

Example 4 Alkylation

Alkylbromide (49.5 mmol) was added to a stirred suspension of 4-(Boc-amino)-piperidine (7) (45 mmol) and K₂CO₃ (264 mmol) in acetonitrile (450 ml). The reaction mixture was heated at reflux for 3 hours and then cooled to room temperature. K₂CO₃ was removed by filtration and the filtrate was concentrated under vacuum to dryness. The residue was dissolved in dichloromethane (90 ml) and water (90 mL) was added. The mixture was stirred and the pH of the mixture was adjusted to pH 10 with NaOH. The organic phase was separated and aqueous phase was extracted with dichloromethane (2×60 mL). The combined organic phase was washed with H₂O (2×90 ml) and dried by K₂CO₃ or a filtration through phase separation paper. Removal of the solvent under vacuum gave product (8) in excellent yield.

Note: the reaction may use an alkylchloride rather than an alkylbromide. If an alkylchloride is used a small quantity of KI was added.

A detailed description of this method is provided in Tien Q. Pham, Ivan Greguric, Xiang Liu, Paula Berghofer, Patrice Ballantyne, Janette Chapman, Filomena Mattner, Branko Dikic, Timothy Jackson, Christian Loc'h, and Andrew Katsifis; Journal of Medicinal Chemistry, 2007, 50 (15), 3561-3572.

Example 5 Boc-Deprotection Via Ion-Exchange Resin

Amberlyst 15 resin was used in the Boc-deprotection. The amount of resin used was calculated based on the number of amino groups in the amine molecules. The ratio is 5:1 molar equivalents of resin to each amino-group in the product. Hence, this molar ratio is 10:1 in the case of diamines and 15:1 in the case of tri-amines.

A very slow dropwise flow rate is critical in all operations involved in resin washing or rinsing to achieve complete deprotection and quantitative or near quantitative yield.

The Boc-protected amine (2, 4, 5, 6 or 8) was dissolved in an amount THF that is sufficient to just cover the resin and the solution was added to the resin. The mixture was heated at gentle reflux overnight without stirring. An aliquot of supernatant was evaporate to dryness and analyse by ¹H NMR to confirm all amine bound to resin. Resin was transferred to a glass column and drained, and then wash with 1× bed volume of THF at a very slow flow rate.

The amine was released from the resin using 2M MeNH₂/EtOH (33%, ˜8M). An equal molar quantity of MeNH₂ with respect to the resin loading was used. The resin was then washed with 1 bed volume of EtOH. In the case of aminoacid derivatives, alcohol was avoided and an aqueous Me₃N/H₂O solution (45%, ˜7.6M) was used to release the amine followed by washing with H₂O (1 bed volume). The combined filtrates were concentrated to dryness to yield the free amine.

The resin was regenerated by washing with 3M HCl in MeOH/H₂O (1:1) (≧1 eq with respect to resin), water (1-2 bed volumes) followed by MeOH (1 bed volume), and then dichloromethane (1 bed volume. The clean resin was finally dried under N₂ or vacuum.

A detailed description of this method is provided in Yun-Shan Liu, Cunxiang Zhao, David E. Bergbreiter, and Daniel Romo; Journal of Organic Chemistry, 1998, 63, 3471-3473.

Example 6

Step 1

2-Hydroxyethylene bromide (9.1 ml, 128 mmol) was added to a solution of 4-aminopyridine (10) (10 g, 106 mmol) in toluene (260 ml). The reaction was heated at reflux for 3.5 hours with stirring and then cooled to room temperature. The formed oil became solid upon cooling. The suspension was filtered and the solid was washed with toluene. The product (11) (22.7 g) was obtained as a pale brown solid at 98% yield.

Note: An alkylchloride or an ω-hydroxy-alkyl chloride is also suitable as a replacement for the bromide compounds in this method.

Step 2

Metallic sodium (1.3 g, 56 mmol) was added slowly to cold MeOH (50 ml) with stirring under nitrogen. The prepared mixture of NaOMe/MeOH was transferred to the hydrogenation vessel and pyridium bromide salt (11) (11.1 g, 51 mmol) obtained from the above reaction was added to the reaction mixture followed by 5% rhodium on charcoal (1.1 g, 10% w/w). The reaction was processed under hydrogen atmosphere (140 psi) at 60° C. overnight. The reaction mixture was filtered through Celite and washed with MeOH (100 mL).

The filtrate was concentrated under vacuum to dryness to confirm complete recovery. The residue was redissolved in MeOH (150 mL) and poured over Amberlyst 15 resin (106 g, 50 mmol). The mixture was heated at gentle reflux without stirring overnight. The resin was transferred to a column and washed with MeOH (150 mL). The amine was released from the resin by using 33% MeNH₂/EtOH (63 mL, ˜0.5 mol) in EtOH (190 mL) and further washed with EtOH (150 mL). Removal of the solvent of the combined ethanolic fractions gave 5.04 g of clear golden oil (69%). Analysis of ¹H and ²³Na NMR showed the desired product (12) free from sodium salt.

The product may also be collected by fractional distillation (collected at 122° C./1.0 mbar).

A detailed description of this method is provided in a) Gordon N. Walker, Miriam Ann Moore and Barbara N. Weaver; Journal of Organic Chemistry, 1961, 26 (8), 2740-2747; b) Tatsuya Ito, Tomomi Ikemoto, Yasushi Isogami, Hiroki Wada, Misayo Sera, Yukio Mizuno, and Mitsuhiro Wakimasu; Org. Proc. Res. Dev., 2002, 6 (3), 238-241; c) ASTRAZENECA AB, Patent: WO2009/35407 A1, 2009; Location in patent: Page/Page column 10; 21.

Example 7 Synthesis of 4-amino-1-piperidineethanol

4-(N-Boc amino)-1-piperidineethanol

4-(N-Boc amino)-1-piperidine (10 g, 50 mmol), bromoethanol (7.1 mL, 100 mmol) and K₂CO₃ (55.2 g, 400 mmol) in acetonitrile (200 mL) were heated at reflux for 5 h. The K₂CO₃ was filtered off and the acetonitrile was evaporated to dryness (reduced pressure). The resulting residue was dissolved in dichloromethane (100 mL) and H₂O (100 mL) was added. The mixture was stirred vigorously and then the phases were allowed to separate, the pH of the aqueous phase was tested (>pH 10, adjust with potassium hydroxide if necessary). The aqueous phase was removed and extracted with dichloromethane (2×100 mL). The combined organic phases were washed with H₂O (2×100 mL) and sat. NaCl (100 mL), dried over Na₂SO₄, filtered and evaporated to dryness (reduced pressure). The product was purified by dry column vacuum chromatography (DCVC) (Pedersen et al.) eluting with methanol/dichloromethane/ethyl acetate (2:9:9), to yield 7.1 g of a golden oil (58% yield) which crystallised on standing to give off-white crystals. ¹H NMR (CDCl₃, 400 MHz) δ 4.43 (br s, 1H), 3.58 (t, J=4.5, 2H), 3.48 (br s, 1H), 2.90-2.78 (m, 2H), 2.51 (t, J=5.4, 2H), 2.24-2.12 (m, 2H), 1.99-1.88 (m, 2H), 1.44 (s, 9H), 1.44-1.35 (m, 2H, superimposed).

4-amino-1-piperidineethanol

The 4-(N-Boc amino)-1-piperidineethanol (13 g, 53.2 mmol) was treated with TFA (26 mL) for 90 mL. The TFA was removed (reduced pressure) and the TEA salt was converted to the HCl salt by treatment with 20% HCl/methanol (130 mL) at ambient temperature for 30 min. The HCl/methanol was evaporated (reduced pressure) and the residue dissolved in H₂O (10 mL). The solution was cooled in an ice-bath and NaOH (10M, 35 mL) added to pH >10. The solution was warmed to RT and stirred for 15 min prior to evaporating to dryness. The residue was triturated with ether/isopropanol (2:1), filtered and evaporated to dryness. The trituration process was repeated until no salt was present in the oil (5×) to yield 6.7 g (87%) of an off-white solid.

Example 8 Synthesis of 4-(2-ethanolamino)-piperidine

This method provides a specific example of the method of Example 1 and the method of Example 6.

1-Boc-4-piperidone

Triethylamine (19.2 g, 190 mmol) was added to a stirring solution of 4-piperidone monohydrate hydrochloride (20.0 g, 131 mmol) in methanol (300 mL) and stirred for 5 min. Boc₂O (34 g, 168 mmol) was added in portions over a 5 min period, followed by DMAP (0.4 g, 3 mmol). The solution was stirred at ambient temperature for 20 h. The methanol was removed under reduced pressure and the crude was dissolved in dichloromethane (100 mL). The organic phase was washed with HCl (2M, 2×70 mL) sat. Na₂CO₃ (70 mL) and sat NaCl (50 mL), dried over Na₂SO₄, filtered and evaporated to dryness to yield 1-Boc-4-piperidone as a white solid in quantitative yield. ¹H NMR (CDCl₃ 400 mHz) δ 3.71 (t, J=6.2 Hz, 4H), 2.44 (t, J=6.2 Hz, 4H), 1.49 (s, 9H).

4-(2-ethanolamino)-1-Boc-piperidine

Na(OAc)₃BH (40.58 g, 192 mmol) was added slowly to a stirring solution of 1-Boc-4-piperidone (15.25 g, 77 mmol), ethanolamine (4.68 g, 77 mmol) and acetic acid (4.6 g, 77 mmol) in dichloromethane (150 mL) cooled in a water bath under N₂ and the solution was stirred at ambient temperature for 18 h. The reaction was quenched by the careful addition of H₂O (75 mL) and the mixture stirred for 45 min. The solution was basified to pH 10 by the careful addition of 25% NaOH (˜150 mL) and stirred a further 10 min. The phases were allowed to separate and the organic phase was washed with H₂O (150 mL) and saturated NaCl (150 mL), dried over Na₂SO₄, filtered and evaporated to dryness to yield the target (17.49 g, 94%) as a clear oil which crystallised on standing. ¹H NMR (CDCl₃ 400 mHz) δ 4.02 (br s, 2H), 3.63 (tr, J=5.2 Hz, 2H), 2.88-2.71 (m, 4H), 2.66-2.54 (m, 1H), 1.91-1.79 (m, 2H), 1.44 (s, 9H), 1.31-1.15 (m, 2H).

4-(2-ethanolamino)-piperidine

The 4-(2-ethanolamino)-1-Boc-piperidine (14 g, 57.3 mmol) was treated with TFA (28 mL) for 90 mL. The TFA was removed (reduced pressure) and the TFA salt was converted to the HCl salt by treatment with 20% HCl/methanol (140 mL, 280 mmol HCl) at ambient temperature for 30 min. The HCl/methanol was evaporated (reduced pressure) to yield a white solid in quantitative yield. ¹⁹F NMR (MeOD) confirmed complete conversion to the HCl salt.

The salt was dissolved in H₂O (10 mL) and cooled in an ice-bath. NaOH (10M, 35 mL) was added to pH >10. The solution was warmed to RT and stirred for 15 min prior to evaporating to dryness. The residue was triturated with ether/isopropanol (2:1), filtered and evaporated to dryness. The trituration process was repeated until no salt was present in the oil (5×) to yield 7.8 g (95%) of a clear oil which solidified on standing.

Example 9

The test results (shown in the accompanying figures) are a comparison of four compounds within general formula (I) with 4-aminopiperidine in terms of their CO₂ absorption at 40° C. (FIG. 2(a)) and CO₂ desorption at 90° C. (FIG. 2(b)). These absorption experiments were carried with CO₂ gas (99%).

The compounds within the scope of Formula (I) used in this example are as follows:

As can be seen from the graphs shown in FIG. 2(a), compounds 1, 2 and 3 have higher capacities for CO₂ loading (200%, 180% and 180% on a mol % basis, respectively) than 4-aminopiperidine (155%). 4-Propylaminopiperidine (Compound 4) has a higher CO₂ loading in absorption than the result shown in FIG. 2(a) Compound 4 formed a large quantity of bicarbonate solid during its CO₂ absorption, which was not able to be measured by ¹³C NMR, hence, the real CO₂ loading was higher than that illustrated in FIG. 2(a). As can be seen from FIG. 2(a) compounds 1 to 4 have faster or at least similar reaction rates in absorption.

Compounds 1 to 4 also displayed better CO₂ release in desorption (FIG. 2(b)). Compounds 1 to 3 desorbed more CO₂ (105%, 100% and 86% on a mol % basis, respectively) at moderate temperatures (90° C.), than did 4-aminopiperidine (67%). Again, the desorption yield of Compound 4 could not be accurately measured due to the inability to accurately measure the CO₂ loading of the starting material.

The results above indicated that the compounds of Formula (I) may improve CO₂ capture capacity (CO₂ absorption and desorption) of known systems. The compounds exhibited a more efficient cycle of CO₂ absorption-desorption, which may lead to significantly lower the energy consumption in CO₂ capture.

These results were also compared with monoethanolamine (MEA) and piperizine (Pz) for their CO₂ absorption and desorption. MEA and Pz are commercially available amines used in industry for CO₂ capture. Aqueous MEA is used as a CO₂ absorber due to its attractive CO₂ loading capacity in g CO₂/g MEA whilst it's desorption is poor and high energy consumption is required. Pz was claimed widely as a promoter in CO₂ absorption by amines, but our study results showed that Pz carbamate was reasonably stable at 90° C., and this limited its capacity as a promoter in CO₂ capture at lower energy consumption.

In FIG. 3, CO₂ absorption and desorption results for Compounds 1 to 4 and 4-aminopiperidine (2M and 1.7M in one case due to the material availability) were compared with MEA (4M) and piperazine (Pz) (2M). An MEA concentration of 4M was chosen in this comparison to match the total amine/nitrogen concentration of diamines (2×2M).

The results of CO₂ absorption at 40° C. are displayed as a ratio of mole of CO₂/mole of amine (FIG. 3(a)) and as a ratio of mole of CO₂/mole of nitrogen (FIG. 3(c)). The results of desorption at 90° C. are also displayed in the same two ways respectively in FIG. 3(b) and FIG. 3(d). Compounds 1 to 4 as a whole showed better reaction rates for CO₂ loading and CO₂ release in absorption and desorption. 1-ethanol-4-aminopiperidine (Compound 1), in particular, stood out during this comparison as shown by its highest loading in absorption and largest release of CO₂ in desorption. It also had the highest reaction rates in both reactions.

Example 10 CO₂ Absorption-Desorption

1. Absorption

An amine solution (2M, 10 mL) was added to a 50 ml jacketed 2-necked pear-shaped flask. The reaction solution was stirred, heated to and maintained at 40° C. with a Ratek Thermoregulator thermostatted bath. The stirring speed, 900 rpm, was kept the same in all absorption and desorption experiments. A condenser was connected to the flask through a Claisen adapter, and an electronic thermometer introduced to monitor the temperature of the amine solution. Hydrated gas of 10% CO₂ and 90% N₂ was introduced to the amine solution through a PTFE tube (0.71 mm ID, 1.78 mm OD) at a total flow rate of 50 mL/min (controlled via a Bronkhorst High-Tech El-Flow mass flow controller). The loading was processed over night (18 hours). A sample was taken for NMR analysis.

The concentration of MEA used in experiment was 4M. This concentration provided same total concentration of amino-groups to that of 2M diamines.

2. Desorption

After the gas supply was removed, the CO₂-rich amine solution obtained from the above absorption was heated at a constant temperature of 90° C. with a Ratek Thermoregulator thermostatted bath. Samples are taken from reaction for NMR analysis at reaction time of 2, 5, 10, 30 and 60 minutes.

3. General Method for Quantitative ¹³C NMR Analysis and Data Processing

NMR samples were placed into a 5 mm (178 mm long, 4.24 mm ID) NMR tube to a height of 40 mm then capped, and an external standard of 1,4-dioxane in a sealed capillary was used in ¹³C NMR analysis (δ_(C) 67.18 ppm, calibrated against an external TMS/CDCl₃ solution). Relaxation times (T₁) of the carbon atoms in the reaction mixture were measured using the standard inversion recovery (“Null”) method. The NMR analytical interscan recycle time was chosen as equal to 5×T₁. NMR spectroscopy was performed at 25° C. The molar ratio of CO₂-loading to amine was calculated based on integration of carbonyl signals and amine aliphatic carbon signals. The weight loading figure then was calculated from molar ratio results. The accuracy of loadings determined in this manner was estimated to be ±3% for amine concentrations of 4 M. The cyclic capacity is the calculated difference between the maximum and minimum CO₂ loading in the process of absorption-desorption cycle.

4. pKa Calculations

Software: SPARC Online Calculator version 4.6—http://archemcalc.com/sparc/

Conditions: 25° C., 0 M ionic strength, aqueous solution.

TABLE 1 CO₂ sequestration in 10% CO₂ and 90% N₂ Cyclic capacity in CO₂ Maximum absorption/ pK_(a) CO₂ loading desorption Amine Amine not Molar Molar in the in the Compound capacity g/g capacity g/g ring ring

1.46 0.51 0.43 0.15 10.47 10.34

1.02 0.35 0.41 0.15 10.41  9.73

1.05 0.29 0.34 0.09 10.44 10.13

1.15 0.25 0.46 0.10 10.46 10.28

1.50 0.39 0.69 0.18 10.43  9.55  (9.51)

1.30 0.40 0.43 0.13 10.47  9.68

1.05 0.29 0.28 0.08 10.41  9.10

1.07 0.27 0.36 0.09 10.44  9.52

1.01 0.21 0.47 0.10 10.46  9.15

1.14 0.39 0.46 0.16  9.68  9.99

1.17 0.36 0.61 0.19  9.70  9.99

1.02 0.31 0.45 0.14  9.11  9.92

1.00 0.28 0.35 0.10  9.52  9.96

0.95 0.21 0.56 0.12  9.15  9.98

1.58 0.49 0.38 0.12 10.65 10.58

1.24 0.38 0.35 0.10 10.62  9.97

0.98 0.20 0.39 0.08 10.65 10.53

0.70 0.19 0.52 0.15 10.71  9.74

1.80 0.43 0.53 0.13 10.63  9.79  (9.53)

1.26 0.41 0.52 0.19 10.65  9.93

1.13 0.29 0.44 0.11 10.62  9.35 ^(a)It has been assumed that the amino acids are in the CH₂COO⁻ form in solution. This yields identical results to the amino acids salts. ^(b)The pK_(a) of any additional nitrogen in the R-group is given in brackets.

Example 10

This example provides ¹H NMR data for examples of compounds of Formula (I).

TABLE 2 ¹H NMR data R =

Et ¹H NMR in d₄- ¹H NMR in d₄- ¹H NMR in d₄- ¹H NMR in d₄- ¹H NMR in d₄- methanol methanol methanol methanol methanol 3.01, 2H, d b, 3.05, 2H, d b, 2.91, 2H, d b, J12.5 2.99, 2H, dt, 3.04, 2H, dt, J₁12.3 J12.8 Hz; 2.62, J12.6 Hz; 2.59- Hz; 2.59, 1H, m; 2.39, J₁12.3 Hz, J₂3.0 Hz, J₂3.0 Hz; 2.60, 2H, q, J7.3 Hz; 2.46, 5H, m; 2H, q, J7.3 Hz; 1.99, Hz; 2.58, 2H, q, 2H, td, J₁12.3 Hz, 2.57-2.49, 3H, m; 2.23, 3H, s; 1.77, 2H, td, J₁12.1 Hz, J7.2 Hz; 2.54, 2H, J₂2.7 Hz; 2.45, 2H, 1.86, 2H, m; 1.22, 2H, d b, J12.8 J₂2.4 Hz; 1.81, 2H, d td, J₁12.4 Hz, q, J7.3 Hz; 2.23, 2H, ddd, J₁24.1 Hz; 1.41, 2H, b, J13.4 Hz; 1.38, 2H, J₂2.6 Hz; 2.41, 3H, s; 2.22, 2H, Hz, J₂12.4 H, ddd, J₁24.6 Hz, m; 1.07, 3H, J7.3 Hz. 2H, d, J6.8 Hz; overlapped; 1.77, J₃4.0 Hz; 1.09, J₂12.4 H, J₃4.2 1.70, 2H, m; 1.60, 2H, m; 1.68, 1H, m; 3H, J7.2 Hz. Hz; 1.05, 3H, t, 1H, m; 1.16-1.05, 1.14, 2H, m; 1.09, J6.2 Hz. 2H, m; 1.09, 3H, t, 3H, t, J7.2 Hz. J7.2 Hz. ^(n)Pr ¹H NMR in d₄- ¹H NMR in d₄- methanol methanol 3.01, 2H, d b, 2.89, 2H, d b, J12.0 J12.5 Hz; 2.58- Hz; 2.58, 1H, m; 2.28, 2.47, 5H, m; 1.86, 2H, m; 2.00, 2H, td, 2H, d b, J12.8 Hz; J₁12.0 Hz, J₂2.4 Hz; 1.49, 2H, sextet, 1.84-1.76, 2H, m; J7.4 Hz; 1.22, 1.55-1.46, 2H, m; 2H, ddd, J₁24.0 1.38, 2H, ddd, J₁24.0 Hz, J₂12.5 H, Hz, J₂12.8 Hz, J₃3.6 J₃3.7 Hz; 0.91, Hz; 0.89, 3H, J7.5 Hz. 3H, J7.4 Hz. (CH₂)₂OH ¹H NMR in d₄- ¹H NMR in d₄- ¹H NMR in d₄- ¹H NMR in CDCl₃ methanol methanol methanol 3.52, 2H, td b, J₁5.4 3.74, 2H, t, J5.6 3.60, 2H, t, J6.3 3.65, 2H, t, J6.2 Hz; Hz, J₂ 0.8 Hz; 3.03, Hz; 3.14, 2H, dt b, Hz; 3.07, 2H, d b, 2.91, 2H, d b, J12.4 2H, d b, J12.1 Hz; J₁12.9 Hz, J₂3.0 J12.6 Hz; 2.60, Hz; 2.59, 1H, m; 2.49, 2.55, 2H, t b, J12.2 Hz; 2.83, 2H, t, 2H, t, J6.3 Hz; 2H, t, J6.1 Hz; 2.09, Hz; 2.46, 2H, td b, J5.6 Hz; 2.66, 2H, 2.58-2.47, 3H, m; 2H, td, J₁11.9 Hz, J₁5.5 Hz, J₂1.1 Hz; td, J₁12.8 Hz, 2.28, 3H, s; 1.78, J₂2.4 Hz; 1.79, 2H, d 2.19, 3H, s; 2.21- J₂2.8 Hz; 2.66, 1H 2H, d b, J12.7 b, J13.3 Hz; 1.39, 2H, 2.17, 2H overlapped; 1.99, Hz; 1.42, 2H, m. overlapped; 1.69, 2H, d b, J12.8 Hz; ddd, J₁24.5 Hz, 2H, d b, J12.8 Hz; 1.36, 2H, ddd, J₂12.4 Hz, J₃3.9 1.57, 1H, m; 1.02, J₁23.8 Hz, J₂12.6 Hz. 2H, ddd, J₁24.4 Hz, H, J₃4.2 Hz. J₁*12.3 Hz, J₂3.8 Hz. (CH₂)₃OH ¹H NMR in d₄- ¹H NMR in d₄- ¹H NMR in d₄- methanol methanol methanol 3.63, 2H, t, J6.2 3.59, 2H, t, J6.2 3.58, 2H, t, J6.2 Hz; Hz; 3.07-2.98, 2H, Hz; 3.05, 2H, d b, 2.91, 2H, d b, J12.4 m; 2.70, 2H, t, J12.3 Hz; 2.61- Hz; 2.60, 1H, m; 2.44, J7.3 Hz; 2.60- 2.47, 5H, m; 2H, t, J7.6 Hz; 2.02, 2.49, 3H, m; 1.94- 2.25, 3H, s; 1.77, 2H, m; 1.81, 2H, d b, 1.85, 2H, m; 1.75- 2H, d b, J13.2 J13.0 Hz; 1.71, 2H, 1.66, 2H, m; 1.31- Hz; 1.72-1.64, m; 1.37, 2H, m. 1.18, 2H, m. 2H, m; 1.42, 2H, ¹³C NMR ddd, J₁24.7 Hz, 61.6, 56.2, 46.0, J₂12.5 Hz, J₃4.2 44.6, 33.8, 33.3. Hz. (CH₂)₆OH ¹H NMR in d₄- ¹H NMR in d₄- methanol methanol 3.52, 2H, t, J6.6 3.57, 2H, t, J6.6 Hz; Hz; 3.05, 2H, d b, 2.95, 2H, d b, J12.3 J12.5 Hz; 2.56- Hz; 2.66, 1H, m; 2.37, 2.42, 5H, m; 2H, m; 2.06, 2H, td, 2.24, 3H, s; 1.80- J₁12.3 Hz, J₂2.6 Hz; 1.73, 2H, m; 1.86, 2H, d b, J12.6 1.56-1.26, 10H, Hz; 1.61-1.51, 4H, m; m. 1.50-1.32, 6H, m. CH₂COOH ¹H NMR in D₂O ¹H NMR in D₂O 3.27, 2H, d b, 3.25, 2H, d b, J12.8 Hz; 3.11, J12.8 Hz; 3.05, 2H, s; 2.83, 2H, t 2H, s; 2.82, 2H, b, J12.8 Hz; 2.71, td, J₁12.8 Hz, 1H, m; 1.97, 2H, d J₂3.0 Hz; 2.40, b, J13.2 Hz; 1.38, 2H, d, J6.8 Hz; 2H, m. 1.87-1.79, 2H, m; 1.76-1.64, 1H, m; 1.25, 2H, m (CH₂)₂N(CH₃)₂ ¹H NMR in d₄- ¹H NMR in d₄- methanol methanol 3.02, 2H, d b, δ 3.00, 2H, m; J13.1 Hz; 2.70, 2.66, 2H, t, J7.2 2H, t, J6.8 Hz; Hz; 2.55, 2H, 2.59-2.50, 2H, m; J₁12.3 Hz, J₂2.1 2.43, 2H, t, J6.7 Hz; 2.47-2.42, 4H, Hz; 2.23, 6H, s; m; 2.23, 6H, s; 1.91-1.84, 2H, m; 1.71, 2H, d b 1.23, 2H, m. J13.0 Hz; 1.67- 1.54, 1H, m; 1.11, 2H, m.

REFERENCES

-   1. Singh, P., Versteeg, G. F., Structure and activity relationships     for CO2 regeneration from aqueous amine-based absorbents, Process     Safety Env. Prot., 2008, 86, 347-359. -   2. Pedersen, D. S, and Rosenbohm, C., Synthesis, 2001, 16, 2431-2434

It will be understood that the invention disclosed and defined in this specification extends to all alternative combinations of two or more of the individual features mentioned or evident from the text or drawings. All of these different combinations constitute various alternative aspects of the invention. 

The claims defining the invention are as follows:
 1. A process for the capture of CO₂ from gas streams, the process including contacting a CO₂ containing gas stream with a compound including: a primary or non-sterically hindered secondary amine group and at least one tertiary amine or sterically hindered secondary amine group; wherein the primary or non-sterically hindered secondary amine and the nearest tertiary or sterically hindered secondary amine group are separated by a carbon chain including 3 or 4 carbon atoms and wherein the compound is a compound of Formula (I)

wherein R¹ is represented by hydrogen, C₂ to C₆ alkanol or C₁ to C₆ alkyl; R² is represented by hydrogen, C₁ to C₆ alkyl, C₂ to C₆ alkanol, —(CH₂)_(n)—NR₆R₇, —(CH₂)_(p)—COOH, —(CH₂)_(p)COOQ, —(CH₂)_(p)-heterocyclic ring containing one to four heteroatoms independently selected from nitrogen, oxygen and sulphur; R³ and R⁵ are independently selected from hydrogen, C₁ to C₄ alkyl, C₂ to C₆ alkanol, —(CH₂)_(n)—NR⁸R⁹; R⁴ is represented by hydrogen, C₁ to C₆ alkyl, C₂ to C₆ alkanol, —(CH₂)_(n)—NR₆R₇, —(CH₂)_(p)—COOH, —(CH₂)_(p)COOQ, —(CH₂)_(p)—SO₃H, —(CH₂)_(p)SO₃Q, —(CH₂)_(p)—PO₃H₂, —(CH₂)_(p)PO₃Q_(s), —(CH₂)_(p)-heterocyclic ring containing one to four heteroatoms independently selected from nitrogen, oxygen and sulphur; x 0 or 1; n is 2 to 6; p is 1 to 6; Q is hydrogen, a metal ion or R¹⁶R¹⁷R¹⁸R¹⁹N⁺; s is 1 or 2 R⁶ and R⁷ are independently selected from hydrogen, alkyl, alkanol, alkylamine or R⁶ and R⁷ together with the nitrogen atom to which they are attached form a ring structure R⁸ and R⁹ are independently selected from C₁ to C₆ alkyl, C₂ to C₆ alkanol, C₂ to C₆ alkylamine, —(CH₂)_(n)—NR₆R⁷, —(CH₂)_(p)—COOH, —(CH₂)_(p)COOQ, —(CH₂)_(p)—SO₃H, —(CH₂)_(p)SO₃Q, —(CH₂)_(p)—PO₃H₂, —(CH₂)_(p)PO₃Q_(s), or R⁸ and R⁹ together with the nitrogen atom to which they are attached form a ring structure; and R¹⁶, R¹⁷, R¹⁸ and R¹⁹ are independently selected from hydrogen or alkyl; with the proviso that when R⁴ is hydrogen, R¹ and/or R² is not hydrogen; when R⁴ is not hydrogen, R¹ and/or R² is hydrogen; when R⁴ and R¹ are both hydrogen, R² is not methyl; and when R⁴ and R² are both hydrogen, R¹ is not methyl.
 2. A process according to claim 1 wherein the compound is a compound of formula (I), wherein: R¹ is represented by hydrogen or C₁ alkyl; R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); R³ is represented by hydrogen; R⁴ is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and R⁵ is represented by hydrogen; with the proviso that when R⁴ is hydrogen, R² is not hydrogen; when R² is hydrogen, R⁴ is not hydrogen; and when R² is hydrogen, R¹ is hydrogen and x is
 0. 3. A process according to claim 2 wherein the compound is a compound of formula (I), wherein: R¹ is represented by hydrogen or C₁ alkyl; R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); R³ is represented by hydrogen; R⁴ is represented by hydrogen; and R⁵ is represented by hydrogen.
 4. A process according to claim 2 wherein the compound is a compound of formula (I), wherein: x is 0; R¹ is represented by hydrogen; R² is represented by hydrogen; R³ is represented by hydrogen; R⁴ is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH, —CH₂COONa, —CH₂COOK, —(CH₂)₂N(CH₃)₂, —(CH₂)₂N(CH₂CH₂)₂O, —(CH₂)₂N(CH₂CH₂)₂S, —CH₂(5-imidazole) or —(CH₂)₂(5-imidazole); and R⁵ is represented by hydrogen.
 5. A process according to claim 3 wherein the compound is a compound of formula (I), wherein: R¹ is represented by hydrogen or C₁ alkyl; R² is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH, —(CH₂)₆OH, —CH₂COOH or —(CH₂)₂N(CH₃)₂; R³ is represented by hydrogen; R⁴ is represented by hydrogen; and R⁵ is represented by hydrogen.
 6. A process according to claim 4 wherein the compound is a compound of formula (I), wherein: R¹ is represented by hydrogen; R² is represented by hydrogen; R³ is represented by hydrogen; R⁴ is represented by —CH₂CH₃, —CH₂CH₂CH₃, —(CH₂)₂OH, —(CH₂)₃OH or —(CH₂)₆OH; and R⁵ is represented by hydrogen.
 7. A process according to claim 2 wherein the compound is a compound of formula (I), wherein: R¹ is represented by hydrogen or C₁ alkyl; R² is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃ or —(CH₂)₂N(CH₃)₂; R³ is represented by hydrogen; R⁴ is represented by hydrogen, —CH₂CH₃, —CH₂CH₂CH₃ or —(CH₂)₂N(CH₃)₂; and R⁵ is represented by hydrogen; with the proviso that when R⁴ is hydrogen, R² is not hydrogen; when R² is hydrogen, R⁴ is not hydrogen; and when R² is hydrogen, R¹ is hydrogen and x is
 0. 8. A process according to claim 2 wherein the compound is selected from the group consisting of:


9. A process according to claim 2 wherein the compound is selected from the group consisting of: 